This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-097792, filed Mar. 29, 2002, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fixing device provided in an image forming apparatus.
2. Description of the Related Art
One type of a device for fixing a toner image on a sheet under heating and pressing in an image forming apparatus that adopts electrophotography is known. This type is configured to fix a toner image on a sheet heated and pressed, while passing through a pair of rollers. Among fixing devices of this type is a fixing device that has an endless belt heated by a heating source. The endless belt runs on one roller and conveys a sheet, while rotating together with the other roller. The sheet is fixed a toner image while passing through between the belt and the other roller.
In a fixing device of heating/pressing type, a sheet with a toner image on it is passed through a pair of rollers facing the image-formed surface of the sheet, toward the heating roller, to fix a toner image on the sheet now efficiently heated. Therefore, the sheet may stick to the peripheral surface of the heating roller or to the surface of the belt running on this roller by causing the heated toner image may act as glue when the sheet is passed through a nip between the paired rollers. In this case, the sheet is no longer conveyed toward the downstream side in a conveying direction. Thus causes jamming of sheets in a fixing device.
This fixing device has a peeling member, which is provided at a sheet exit side of the pair of rollers. The peeling member guides the sheet coming from the nip between the paired rollers, in a direction away from the heating roller. Thus, the peeling member prevents the sheet from being left stuck on one of the paired rollers.
A gap must be provided between the forward end of the peeling member and the peripheral surface portion of the heating roller, so that the sheet passed through the paired rollers may be properly guided in a direction away from the heating roller. If the gap is too large, the sheet may enter into the gap, causing jamming of sheets. If the gap is too small, the forward end of the peeling member may contact the peripheral surface of the roller, inevitably damaging the peripheral surface portion of the roller.
Where, conventionally, the peeling member, if provided, is so positioned that the forward end of the peeling member provides a gap of necessary size, jointly with the peripheral surface portion of the roller. In this case, the peeling member is bolted to the body of the image forming apparatus. If the peeling member is secured to the body of the image forming apparatus, it is difficult to position the peeling member to create a gap that corresponds to a proper space between the forward end of the peeling member and the peripheral surface portion of the roller. After the peeling member is detached from the body, it is difficult to secure the peeling member again at the original position on the body to provide a proper gap between the forward end of the peeling member and the peripheral surface portion of the roller.
The peeling member is bolted to the body. It must be unbolted from the body to remove to eliminate sheet jamming. After the sheet jamming is eliminated, the peeling member must be bolted again at its mounting position of the body. It is cumbersome and troublesome to remove the peeling member from its mounting position and fix it at the original position.
Once jamming of sheets occurs between the peeling member and the roller in the fixing device, the peeling member must be detached from the body. After the sheet jamming is eliminated, the peeling member must be mounted at the original position. Thus, a cumbersome operation and a lot of time are required to remove the jammed sheets.
The present invention provides a fixing device, which can easily position the peeling member relative to the roller and also can easily set the peeling member at a predetermined position or remove it from this position.
A fixing device according to an embodiment of the present invention has a first roller, a second roller configured to sandwich and convey the sheet together with the first roller to fix a toner image on a sheet, a peeling member located on a sheet exit side relative to the first and second rollers and configured to guide the sheet from a nip between the first roller and the second roller, away from the first roller, and a positioning mechanism configured to position the peeling member. The positioning mechanism has a support shaft which is located on a sheet exit side relative to the first roller in a state parallel to a central axis of the first roller, a positioning member which carries the peeling member, which is supported by the support shaft to be rotatable in a direction toward and away from the roller shaft of the first roller, and which is configured to abut the outer peripheral surface portion of the roller shaft, and an elastic member which is configured to urge the positioning member in a direction to abut on the peripheral surface portion of the roller shaft of the first roller.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.